In many plastic molded tanks, such as fuel tanks, instrument and fluid fitting attachments are typically made by a welding process (hot plate welding, ultrasonic welding or friction welding) or by inserting a ring or component into a molding tool and overmolding around it to create a mechanical bond for retention. These processes are difficult in that they require inserting components into a hot tool or require complicated secondary operations for maintaining good plastic welding integrity.
In some molded tanks, such as those molded by roto-molding processes, which are typically used for low volume tanks (marine applications, motor cycles, other recreational vehicles), the material used cannot be welded after the molding process due to material degradation with low density polyethylene. Further complicating the above-noted factors is that many polymeric materials have the tendency to creep (move over time) or distort when exposed to liquid hydrocarbons such as gasoline, diesel oil or other vehicle fuels.
It is desirable to provide a polymeric tank assembly having a more reliable method of attaching various parts, such as nozzles, drop-in fuel pumps, and level indicators.